A method is known from WO 99/16650 where the characteristic curve is also established using a special method without force sensor. In that case, an equivalent force value is established which is calculated solely from measured values for the actuator position and actuator torque, as well as their time derivation and various constants. Unknown influencing variables such as friction and damping are calculated using a special periodical activation signal as well as an extensive analysis of the measurements. The disadvantage of this method, in particular, is that all of the measured values for a complete period of the activating signal have to be stored temporarily and then, in a further stage using a complicated analysis process, provide a value of the characteristic curve to be established and representing the above mentioned relationship. This means that this method is not capable of real-time function and also acts on the assumption that the application point is known, i.e. the actuator position where the brake linings are just in contact with the disc but are not yet applying any force. Although a solution to this is provided in WO 99/16650, it requires a very high resolution phase incremental encoder which is very expensive.